Effects of Estrogens on the Actions of hERG

Abstract

Regulation of cardiac ion channels by sex hormones accounts for gender-differences in susceptibility of Torsades de Pointes (TdP) arrhythmias associated with QT prolongation, that is: women are more prone to develop drug-induced arrhythmias which can lead cardiac sudden death. We previously found that β-estradiol (E2) directly interacts with a drug-binding site, F656 of the hERG channel, and alters the effect of a selective hERG blocker. Although these actions were observed for other estrogens, the effect of estrogen on other drugs has been unknown. In this study, to reveal impacts of the actions of estrogens on hERG currents, we compared the hERG screen data in the absence and the presence of estrogens using manual and automated patch-clamp experiments. HEK293 cells stably-expressing the hERG channels were seeded into 384-well plates, and were cultured in a steroid-free condition. Whole-cell hERG currents were recorded by the patch-clamp technique with SyncroPatch 384i (Nanion). Effects of 22 compounds were assessed by percentage changes of hERG peak tail currents with or without estrogens (E2, estrone sulfate; E1S, and ethynylestradiol; EE2) and by molecular docking simulations. Our hERG screening depicted that some estrogens showed distinct effects on respective blockers. Estrogens did not change the degree of hERG block by most of compounds. However, we have newly found that inhibitory action of one drug was increased by E2, and that of another drug was decreased by EE2. This means that specific combinations of an estrogen and a hERG blocker can alter the hERG blockade significantly. Indeed, some combinations resulted in larger hERG currents. This study suggests potential risks using estrogen therapy/medication and the necessity of taking sex hormonal differences into consideration for more accurate prediction of QT prolongation proclivity of drug candidates.